Says you're planning to lie under the forks with an electric drill, pushing the bit into the bottom of the steering stem? I'm guessing you don't know about lubrication and cooling when drilling steel? Try entering something like, "drilling steel" into YouTube and watch a couple of the linked videos ... Without copious amounts of cutting fluid, the drill bit will heat up and blunt very rapidly.

Also ime, the axis of the hole is highly unlikely to align with the axis of the steering stem. Having tapped the hole, your bolt on-bracket will be at right-angles to the hole, not the steering stem ...

Having drilled and tapped a hole in the steering stem or lower yoke casting and bolted on the bracket, you can't be sure there'll be clearance for the heatsink under the headlamp shell. Even Triumph couldn't guarantee it, is why the heatsink in your images has that stepped bracket ...

Premium Member

Either a strip that is roughly the width of the height of the bottom yoke (sorry about the mix of height/width!!)
Or something wider that you can cut to make a T shaped bracket.
Width wise, fit it using the bottom yoke pinch bolts, and if using the T shape, bend to give a mount for the egg.

Registered

Just leave the zener in place and disconnect it. I left mine in place for future generations (I can only hope the bike survives). My podtronics is actually mounted on the inside of the zener heat sink (I have the kind by the battery). You can stash that thing in a lot of places.